The present invention relates to a microcomputer-based electronic control system for controlling the charging system in a motorized vehicle.
The basic function of the charging system in an automobile is, of course, to maintain a substantially constant battery voltage. A conventional automotive charging system includes two main components, the alternator and the voltage regulator. The alternator interfaces directly with the battery and is the source of energy that charges the battery. The output of the alternator is directly proportional to the current flow through its field windings at a given alternator RPM. The function of the voltage regulator is to control the output of the alternator in accordance with the voltage level of the battery by controlling current flow through the field windings of the alternator. In particular, when the battery voltage drops below a specified voltage level, the voltage regulator is adapted to sense this condition and apply current to the field windings of the alternator to thereby provide a charging current from the alternator to the battery. When the battery voltage reaches the desired voltage level, the voltage regulator interrupts current flow to the field windings of the alternator to stop the charging process. In practice, this procedure may repeat itself many times per second and is referred to as modulating the alternator field current.
The desired voltage level to which a battery is charged is dependent on the temperature of the battery. At sub-zero temperatures it is more difficult for the battery to hold a charge, and therefore the battery is charged to a higher voltage. Conversely at high temperatures the battery need only be charged to a lower voltage in order to hold a proper charge. To account for this temperature dependency, voltage regulators typically include a temperature sensing device that is physically associated with the voltage regulator to provide a temperature feedback signal that approximates the temperature of the battery.
Conventional voltage regulators comprise either a separate unit that is mounted to the firewall, shock tower, or other convenient location in the engine bay, or a unit that is constructed integral with the alternator. Both approaches possess disadvantages with respect to temperature and system load compensation. The separate voltage regulator approach, while providing reasonably accurate battery temperature tracking, involves the manufacture, assembly, and maintenance of an additional component and therefore is not widely used. The more common integral voltage regulator, however, assumes the temperature of the alternator and therefore does not accurately reflect battery temperature. Moreover, to provide a separate temperature sensor located near the battery would extract a substantial cost penalty.
To provide the voltage regulator with a signal indicative of battery voltage, it is desirable ideally to connect a battery feed sense line from the voltage regulator directly to the positive battery terminal. However, as conventional voltage regulators contain fairly low impedance devices, this would present an excessive battery drain when the ignition is off. Consequently, voltage regulators typically have their sense wires connected through the ignition switch or related relay. Since there exists a limited number of battery feeds to the ignition switch, the battery sense wire must therefore share the sense point with other loads (e.g., blower motor, light, etc.). As these common loads increase their current requirements, it similarly increases the possibility of substantial voltage drops across each connection, thereby lowering the voltage at the sense point. It can thus be seen that load compensation for conventional voltage regulators can depend significantly on the particular placement of the battery voltage sense wire to the voltage regulator.
It is the primary objective of the present invention to provide solutions to these problems by providing an improved charging system that eliminates the conventional voltage regulator and utilizes in its place the intelligence of a microcomputer already present on the vehicle for controlling engine operation. More particularly, it is an object of the present invention to utilize the sophisticated control capability of the microcomputer to regulate the output of the alternator.
In general, the present invention provides a computer-controlled charging system which includes a logic module containing the microcomputer and a separate power module containing the high current circuitry that interfaces with the alternator field windings, the battery sense point, and the battery temperature sensor. The logic module, which includes the electronics used to control engine operation, directly senses engine RPM, vehicle speed, and throttle angle or position. In addition, via the power module, the logic module is also supplied with information relating to battery voltage and battery temperature. By processing these inputs in a manner described in detail hereinafter the logic module is able to precisely regulate the output of the alternator and hence the charging of the battery. Moreover, by utilizing the intelligence of the microcomputer and the additional information regarding the operation of the vehicle available to the microcomputer, the present invention is capable of providing more efficient control of the alternator.
Specifically, the microcomputer in the preferred embodiment is adapted to sense when the vehicle is decelerating and charge the battery to a higher voltage level during such periods of deceleration. This serves to more efficiently utilize some of the energy represented by the momentum of the vehicle which is normally wasted in the converted form of heat as the vehicle is braked. Also, by charging the battery during deceleration, an additional load is placed on the engine which also serves to assist in slowing the vehicle.
In addition, the microcomputer is preferrably adapted to charge the battery to a higher voltage level during the initial few minutes of operation after start-up of the engine to insure proper charge retention by the battery on short trips. Similarly, the present invention contemplates more precise control of engine RPM at idle to handle the charging load of the engine. This feature is, of course, particularly useful with the smaller four-cylinder engines widely in use today.
Furthermore, the present charging system provides improved voltage control at high and low temperature extremes by programming into the microcomputer upper and lower battery voltage limits to prevent damage to the vehicle lighting systems or other battery voltage sensitive components at such temperature extremes. By virtue of the input signal provided to the microcomputer relating to throttle position, the charging system in the preferred embodiment can also reduce or turn off altogether the charging function at wide-open throttle (WOT) settings to help minimize engine loading when maximum engine output is being demanded. In addition, the intelligence of the microcomputer used in the present charging system allows for improved diagnostic capability to promptly identify the existence of, and more accurately diagnose the cause for, a failure in the charging system.